There are generally two major products in metallized-film capacitors; the one uses metallic foil as its electrodes, and the other one uses metal deposited on dielectric film as its electrodes. The metallized-film capacitor using deposited metal as the electrodes (hereinafter referred to as a deposited electrode), in particular, can be downsized because of its smaller electrodes than those of the other one, i.e. the capacitor using metallic foil as electrodes, and is more reliable with respect to dielectric breakdown because of its self-healing performance proper to the deposited electrode, so that it has been widely used. Meanwhile, the self-healing performance can recover the function of a capacitor when a short occurs at a defective insulation, because an energy produced at the short vaporizes and scatters the deposited electrodes around the defective insulation, thereby insulating the defective insulation. Such metallized-film capacitors are described hereinafter as prior art 1–3 and with reference to FIGS. 11–16.
As shown in those drawings, a first metallized film includes deposited electrode 110, which is formed by depositing metal on a film, on its one surface except at an edge where insulation margin 4a occupies. Deposited electrode 110 has plural divisional electrodes 2a which are divided by non-deposited slit 52a having no deposited metal, and is coupled in parallel to non-divisional electrode 1a via fuse 7a disposed to slit 52a. A second metallized film includes deposited electrode 210 formed on the entire one surface of dielectric film 3b except an edge on the opposite side to insulation margin 4a, which edge is occupied by insulation margin 4b. Deposited electrode 210 is non-divisional electrode 1b discussed above. The foregoing two metallized films are taken up or wound together such that insulation margins 4a, 4b do not overlap with each other, or the two films are laminated alternately, then metallized contacts 6a and 6b are formed on deposited electrodes 110 and 210 respectively forming connecting sections. FIGS. 15, 16A, and 16B show insulation margin 78a. 
The self-healing performance previously discussed of the metallized capacitor becomes better as the thickness of deposited electrodes 110 and 210 decreases, and the deposited electrode can be scattered by less energy. Thus as shown in FIG. 15, the thickness of the deposited electrode of effective electrode 2a, which form a capacity defined by width “W”, is thinned, while the thickness of deposited electrode 110 at the connecting sections to metallized contacts 6a and 6b is thickened, so that thick-film electrode 11a is formed. This construction is called a heavy edge structure, which has been also widely used. This structure allows heightening a withstanding voltage of a capacitor, so that capacitors can work at a higher voltage environment.
Slit 52a having no metal at all divides the deposited electrode into plural divisional electrodes 2a, and fuse 7a disposed parts of slit 52a couples divisional electrodes 2a to each other in parallel. At the self-healing, this construction blows out fuse 7a around the defective insulation with a short-circuit current, thereby isolating the defective insulation from the electric circuit. In other words, this construction includes a self-maintaining function.
In recent years, the following idea is proposed: as shown in FIGS. 13, 14A, and 14B, slits 52a are prepared in a lattice form, and the deposited electrode is finely subdivided, and they are coupled to each other in parallel with fuses 7a, so that lattice-like divisional electrodes 32a are formed. This construction allows decreasing an area of each one of divisional electrodes 32a, so that a capacity decrement at blowout of fuse 7a becomes smaller. Limitation of fuse shape or an area of each one of divisional electrodes 32a within a certain range allows increasing the insulation-recovering performance of the deposited electrodes. Therefore, the metallized-film capacitor can obtain a high-voltage gradient performance, to be more specific, a withstanding voltage at a thickness of 1 μm of dielectric film is heightened.
For instance, Japanese Patent Unexamined Publication No. H04-225508 discloses the following structure: Use of lattice-like divisional electrodes, of which divisional slits have free-ends rounded, allows obtaining a voltage gradient twice as much as that of a metallized-film capacitor free of divisional electrodes. Another Japanese Patent Unexamined Publication No. H05-132291 discloses the following structure: a metallized-film capacitor having lattice-like divisional electrodes, each of which has a surface area ranging from 10 to 1000 mm2, can achieve a voltage gradient of 130–350 V/μm with a dc (direct current).
However, although the conventional metallized-film capacitor discussed above achieves a self-maintaining function using a fuse function, the fuse generates heat because of a current running during the operation, so that a temperature of the capacitor increases. In other words, in the case of a constant dc kept applying to the capacitor, the heat can be neglected because a current does not run through the capacitor. On the other hand, if a ripple current, charge or discharge current, or surge current runs through the capacitor, the current runs through the fuse, thereby generating heat. Temperature rise in a capacitor will lower a withstanding voltage, so that a long-term reliability is also lowered.
The lattice-like divisional electrodes previously discussed has a number of fuses, which invite a greater temperature rise, and as a result, its withstanding voltage as well as long-term reliability is substantially lowered. This is a crucial problem.
The heavy-edge structure previously discussed has a thin deposited film, so that heat generated by fuse becomes greater. A wider width of the fuse or parallel arrangement of the fuses will reduce the heat; however, those measures lower the self-maintaining function instead. A satisfactory solution is thus still needed.
In the case of using a capacitor for smoothing application in an inverter control circuit, a large ripple current runs through the capacitor while a dc voltage is applied across the capacitor. In this case, the withstanding voltage of this capacitor is lowered by temperature rise due to the ripple current. When this capacitor is used in an automobile among others, this problem becomes crucial because the environmental temperature is basically high.